1. Field of the Invention
This invention relates in general to the field of implanted bone fixation devices and in particular to a device for operative reduction and internal fixation of femoral head, neck or intertrochanteric fractures.
2. Description of the Prior Art
Fractures across the head, neck or intertrochanter of the femur whereby the broken portion is separated from the femur are fairly common especially in older people. Any person having a minimal knowledge of the hip bones and joint is well aware of the significance of such a fracture. The peculiar configuration of the femur at the hip joint in conjunction with the severity of the cyclic loads imposed at the hip joint during normal activities such as walking leads one to wonder how a femoral break at the hip joint can ever be successfully repaired through surgery. Fortunately, the success of surgical reduction and fixation is fairly high due, in part, to the availability of some excellent internal fixation devices, one of which is commonly known as a compression hip screw, and advanced modern day surgical techniques. indeed, it is not uncommon for a patient to begin walking almost immediately following an operation involving internal fixation of the femur at the hip joint.
This is not, however, to imply or suggest that one hundred percent success is continually attained. Nor is it suggested that present-day compression hip screws do not fail. And, it is not suggested that the present day compression hip screws assure success of bone reduction and fixation. Although many factors are involved, such as the nature of the break, the healing capabilities of the patient, the expertise of the operating surgeon, etc., some failures are attributable to the compression hip screw itself because of the many conflicting requirements imposed on such devices.
Basic components of a compression hip screw include a lag screw, a barrel hip screw plate and a compressing screw. The lag screw comprises a long shaft having lag threads on one end. The lag screw extends across the break and into the femoral head. It is used to reduce the fracture and permit impaction of any fragments. The barrel hip plate engages the free end of the lag screw and extends down and is secured to the lateral side of the femur. The lag screw and the plate are generally at an inclined angle of 135.degree. or more, relative to each other. The compressing screw connects the lag screw to the plate and allows for compression (reduction) of the fracture.
It is highly desirable that the lag screw remain rotationally fixed relative to the plate in order to assure that the broken fragment does not rotate relative to the femur. A key and keyway arrangement between the lag screw and the barrel of the plate is one way the prior art compression hip screws prevent such relative rotation. However, because the lag screw is buried within the trochanter, the neck and the head of the femur during surgery, it is extremely difficult for the operating surgeon to "find" the shaft of the lag screw for its fit up with the barrel on the plate. Finding the keyway on the shaft is even more difficult. Once key and keyway are mated, the problem is not solved. There is a high probability that the plate is then not axially aligned with its mating surface along the length of the femur. This necessitates removal of the plate, rotation of the lag screw, and then reinsertion of the plate. This procedure may be required to be repeated a number of times until alignment is achieved. Each time, the free end of the lag screw must be located and the key-keyway fit up accomplished. This is obviously not a satisfactory procedure.
The difficult nature of the above-stated problem has led to the development of and use of the "keyless" compression screw. As the name implies, no mating key-keyway arrangement is used for the lag screw-barrel fit up. Without a doubt, this keyless arrangement eliminates the above-described alignment problem, but in so doing, it provides no assurance that the femoral head will not rotate relative to the femur (or the lag screw relative to the hip screw plate) during the operation or during the postoperative period of bony healing.
In other words, the "keyless" solution simply ignors relative rotation problems. The adverse consequences of relative rotation including femoral head rotation which in addition to patient discomfort, may include delayed healing or nonunion of the bone and appliance bending, breaking or pull out from the bone. Obviously, not a satisfactory result, indicating that relative rotation should not be ignored.
Another troublesome aspect of the prior art compression hip screws is the necessity of the lag screw to slide relative to the barrel of the plate during surgery and during postoperative healing and union of the bone. To attain proper reduction of the break and proper impaction of the broken fragments, the lag screw must slide within the barrel portion of the hip screw plate. A key-keyway arrangement, even if accurately aligned, inhibits sliding and therefore hampers proper reduction and impaction. Bone absorption during the post-operative period also requires sliding between the barrel and lag screw. Again, the key-keyway arrangement opposes such movement. The keyless compression screw on the other hand, allows such relative sliding, but as stated above, it has certain disadvantages of its own.
Accordingly, it is a primary object of the present invention to provide an internal hip fixation device for fractures of the proximal portion of the femur which is keyless and therefore easy to install but prevents relative rotation between the lag screw and the barrel of the hip screw plate and the compressing screw.